This invention relates to an apparatus for creating, controlling and measuring electrostatic discharges in combustible materials, such as solid rocket fuel, in order to determine the charge necessary to create sustained ignition in these materials. In particular, the invention relates to a testing apparatus for controlling the duration of a spark applied to combustible materials.
The sensitivity of rocket propellants to electrostatic discharge (ESD) has been and is a major and continuing concern to the propulsion industry. The build-up and subsequent discharge of electrostatic charge on energetic materials used in ammunition and propulsion systems can pose a severe hazard during the handling of these systems. This hazard arises when energetic materials are charged to a potential where breakdown of the material occurs or when a change in grounding allows the breakdown of an existing charge in the material to occur. Discharge processes generate charge carriers, which in turn reduce the impedance of the energetic material and result in a rapid current increase. These processes can lead to arcing and the establishment and growth of discharged paths, followed by a catastrophic discharge. Such reactions lead primarily to pressure and temperature increases in very narrow discharge paths that may in turn induce ignition, sustained combustion or even detonation. Consequently, it is essential to predict a propellant's response to various levels of induced voltages and to study phenomena associated with electrostatic discharges in order to minimize the danger these discharges present to those working with energetic materials.
Being able to predict a propellant's response to given energy levels is important in assessing the ESD hazards of propellants and rocket motors. Tests used in the prior art, however, have the disadvantage of requiring considerable human judgment to assess the amount of damage caused to the sample by the ESD, thereby entering errors into the analysis of ESD hazards. These tests also may include energy delivered to the sample after ignition has occurred, causing errors in the determination of the sample's actual ignition point. Finally, the prior art tests may give erroneous results at high energy levels when the electrostatic discharge occurs over such a short period of time that the material is expelled before it has time to ignite.